1. Field of the Invention
The present invention relates to a gas-driven cutting apparatus and a table for supporting a workpiece in a manner suitable for cutting by the gas-driven cutting apparatus. The gas-driven cutting apparatus forces hot gases in a downward direction into the table in order to cut the workpiece.
2. Discussion of Background Information
Gas-driven cutting (flame cutting) apparatuses perform cutting processes such as oxyfuel cutting and plasma-arc cutting. Oxyfuel cutting is typically used to cut steel workpieces by burning fuel gas in preheated oxygen to raise the workpiece to a kindling temperature (1,500 F). A separate stream of cutting oxygen is driven downward onto the workpiece in order to cut the same. In plasma-arc cutting, a high velocity jet of hot (50,000+F) ionized gas is utilized to sever the workpiece. Plasma cutting can be used to sever almost all conductive materials, including carbon, alloy, and stainless steels, along with most nonferrous metals and alloys. While oxyfuel cutting will have difficulty in properly cutting stainless steel and cast iron, the plasma-arc cutting can cut such materials with little trouble.
In both oxyfuel cutting and plasma-arc cutting, a stream of gas is forced downwardly (at a predetermined flow rate) upon a workpiece. Thus, contaminating/polluting gases are produced at a rate related to the flow rate of the downwardly forced gases produced during the cutting process. As an example, in performing manual oxyacetylene cutting, a gas-driven cutting apparatus will typically generate between 45 and 55 cubic feet per hour (CFH) of oxygen along with 7 to 9 CFH of acetylene in order to cut a plate that is 1/8 inches thick, and between 720-880 CFH of oxygen along with 42.3 to 51.7 CFH of acetylene in order to cut a steel plate that is 12 inches thick. A water-injection plasma-arc cutter will typically generate a total gas flow of 110 cubic feet per hour (CFH) in order to cut mild steel having a thickness of between 0.035 and 1/4 inches, using nitrogen as the plasma gas.
Stationery open-top tables are frequently provided to support workpieces being cut by gas-driven cutting apparatuses, such as oxyfuel cutting and plasma-arc cutting apparatuses. Such stationary open-top tables collect molten metal and other solid by-products which drop from the workpiece as it is being cut. In addition, such tables are utilized to collect the scrap pieces that fall into the table. Some stationary open-top tables hold water for collecting dust and other contaminants that fall into the table and for preventing such dust and contaminants from being "kicked up" into the air during the cutting process (due to the forced gases being driven down into the table).
U.S. Pat. No. 3,743,260 (Alleman, et. al) discloses an anti-polluting waste collector for a burn table, adapted for supporting a workpiece beneath a flame cutting machine. The waste collector includes an open tank containing a liquid maintained at a predetermined level therein and a grating disposed across the tank opening.
U.S. Pat. No. 4,162,060 (Anderson et. al) discloses a semi-automatic water table which includes a water-holding tank, a mechanism for changing the water level in the tank and a mechanism for collecting swarf or waste material. The burning table includes a plurality of burning bars positioned in the tank above the water level changing mechanism.
Yet simpler burn tables have been provided which comprise a sealed tank for holding water therein and which support a workpiece for cutting by a flame cutting machine. Such burn tables do not include elaborate mechanisms for removing slag and other wastes that are formed during the cutting process. In these simpler burn tables, waste materials may be removed by simply removing the grating on the top of the table and manually removing the waste materials from within the table on a periodic basis.
Many burn tables have large surface area open tops (e.g., 8 ft..times.8 ft., 10 ft.times.15 ft, or larger) and a plurality of slats upon which a workpiece may be placed for cutting. Such burn tables facilitate cutting of workpieces in any position along the top of the table without limitation as to the cutting path utilized by the cutting apparatus. In order to remove the gases, fumes, and minute contaminants that are produced during the cutting process with such tables, overhead air cleaners have been utilized for removing such pollutant matter after it has already been introduced into the atmosphere. Such overhead air cleaners typically take a long time to filter the pollutant matter from the atmosphere, and typically take an hour or longer after the atmosphere is contaminated to remove most of the contaminating particles and fumes. Thus, if torch cutting is performed on a table for eight hours, the work area will remain polluted for nine hours. An industrial air cleaner that may be used in a manufacturing plant for this purpose is the Tepco model M3000 heavy duty industrial air cleaner.
Down draft tables, which have small surface area open tops, are available, and create a powerful draft across the upper surface of the table in order to suck the gases and dirt down into the table. Such down draft tables utilize powerful fans to create a draft over table tops having small surface areas.
Various pollution removal mechanisms have been provided for specialized burn tables, in which a fume removal conduit is provided at a location adjacent to where a cut is being performed on a workpiece. For example, U.S. Pat. No. 3,539,168 (PFEUFFER) discloses equipment for flue gas extraction and cutting of continuous casting installations. The workpiece (a continuous casting) is supported on spaced support elements. The cutting device moves synchronously above the workpiece, and cuts the workpiece at a location between a pair of the support elements. At a location at which the workpiece will not be cut, a completely closed off roof-shaped plate is provided to cover a space 21. When the workpiece is at a cutting location, two single plates 28, 28a are arranged over the space 21. A spacing is provided between the plates because a continuous covering plate in the operating range of the cutting torch would become damaged by the cutting flame. The fume gases that are created in and near the opening are concentrated by the shielding of space 21 and may be drawn off from the space.
U.S. Pat. No. 4,058,299 (LINDKVIST) discloses an apparatus for removing polluting matter in connection with a flame cutting table. A moveable suction box is provided below the table and means are provided for reducing the speed of jets directed from the flame cutters toward the interior of the suction box.
In the apparatus of U.S. Pat. No. 3,539,168 (PFEUFFER), a collecting chamber is provided immediately below the position at which the workpiece is cut. In that patent, the workpiece is moved, while the chamber remains stationary. In U.S. Pat. No. 4,058,299 (LINDKVIST), the workpiece is stationary, and a suction box is moved so that it is directly underneath the position at which the workpiece is being cut. Thus, the first patent moves the workpiece so that it is cut over a localized collecting chamber, and the second patent moves a suction box so that it is directly underneath the position of cutting of the workpiece. In each of these patents, a suction device is provided which is localized and thus can provide a higher suction power in order to remove the fumes and particulate matter.
There is a need for a cutting table having an open top with a large surface area, which can collect large pieces of slag and other waste materials that are dropped from the workpiece while it is being cut, and that can also remove gases, fumes and other minute particles before they are introduced into the atmosphere while cutting is being performed. There is a particular need for such a flame cutting table that can facilitate cutting workpieces of all sizes at various positions throughout the open top of the table, without the need to provide a localized suction chamber.